Motion & Colour Perception

Question 1

What are the functions of motion perception?

Answer 1

• Break camouflage
• Attract attention
• Segregate objects from background
• Interpret events
• Determine structure of objects
• Determine what actions people are performing

Question 2

Describe breaking camouflage

Motion Perception

Answer 2

• Something camouflaged can be virtually invisible
  
  • Until it moves

Question 3

Describe attracting attention

Motion Perception

Answer 3

• Something moves
  
  • Attention is attracted to it

Question 4

Describe interpreting events

Motion Perception

Answer 4

• Seeing how objects interact
  
  • Infer causality and social relationships

Question 5

Describe infering structure

Motion Perception

Answer 5

• Kinetic Depth Effect
  
  • Motion helps in determining the shape of a moving object

Question 6

Describe interpreting actions

Motion Perception

Answer 6

• Ambiguous static pose → Moving = Actions and intentions made clear
• Demonstrated using point-light walkers

Question 7

What are point-light walkers?

Motion Perception

Answer 7

• Lights placed on a person’s joints
• Have them perform an action
• Recorded so that only light can be seen
• Guess what action was performed from video

Question 8

What is akinetopsia?

Answer 8

• No longer able to perceive motion
  
  • Damage to brain responsible for motion perception

Question 9

Describe the case of LM

Answer 9

• Akinetopsia
• Difficulties with…
  
  • Pouring a cup of tea
  • Crossing the street
  • Following speech
• Could see that things had moved
  
  • Couldn’t see them moving

Question 10

When do we perceive motion?

Answer 10

• Real Motion → Actual movement
• Illusory motion → Not actual movement
• Motion aftereffects
• Induced Motion → Moving background = Stationary object appears to move

Question 11

Describe apparent motion

Answer 11

• Series of stationary images presented in succession
  
  • Gives impression of motion
• Dots sufficiently close together
  
  • Can’t be too far apart
  • Alternation rate can’t be too fast
• As separation increases alternation rate tends to decrease
• Insensitive to colour changes

Question 12

What is induced motion?

Answer 12

• Nearby object (usually large) affects perceived motion of second object (usually small)
• Or causes a second object to appear to move

Question 13

What is motion induced blindness?

Answer 13

• Motion causing things to disappear

Question 14

What is motion induced change blindness?

Answer 14

• Harder to notice changes
• Steps (?)
  
  • Colour changes attract attention because of transient signals associated with the change
  • Movement → Transient signals with all objects (not just ones changing)
  • Attention no longer drawn preferentially to changing objects
  • Changes not noticed

Question 15

Describe motion illusions

Answer 15

• Inform us of the processes underlying motion perception
• Higher contrast = Faster
• Lower contrast = More slowly

Question 16

What is the function of colour perception?

Answer 16

• Suggested that colour vision evolved primarily to help humans search for things
• Making judgements
  
  • Ripeness of fruits
• Poisoness animas are often coloured

Question 17

Describe the physics of colour

Answer 17

• Visible light is electromagnetic radiation with wavelengths varying about 400nm to about 700nm
  
  • White light is a mixture of all wavelength

Question 18

Describe the colour of opaque objects

Answer 18

• Opaque objects → Object that light cannot pass through
  
  • Not at all transparent
• Colour determined by the light that it reflects
• Examples
  
  • Absorbs blue light but reflects red light = Looks red
  • Reflects all light = Looks white

Question 19

Describe the colour of transparent objects

Answer 19

• Colour determined by the colour it transmits
  
  • Absorbs blue but transmits red = Looks red

Question 20

Describe mixing (blue and yellow) paint

Answer 20

• Blue + Yellow
  
  • Blue absorbs red but reflects blue and green
  • Yellow absorbs blue but reflects red and green
• Mixing creates a mixture that absorbed red and blue but reflects green
  
  • Looks green

Question 21

Describe mixing light

Answer 21

• Red + green = Yellow
• Blue + yellow = White
  
  • Contained blue, green and red
  • White light is a mixture of the three colours

Question 22

What is the Munsell Colour System?

Answer 22

• Colours categorised according to…
  
  • Value (lightness)
  • Hue (colour)
  • Chroma (saturation)

Question 23

What is the trichromatic theory of vision?

Answer 23

• Retina has photoreceptors known as…
  
  • Rods
  • Cones

Question 24

Describe rods

Trichromatic Theory of Vision

Answer 24

• Cannot distinguish between colours and are active only at low light levels
  
  • Normal light = Inactive (only cones active)

Question 25

Describe cones ## Footnote Trichromatic Theory of Vision

Answer 25

* Three types that response maximally to a different wavelength * S cones - 419nm (blue) * M cones - 531nm (green) * L cones - 558nm (red) * Comparing relative activities = Distinguish colours

Question 26

Describe colour matching

Answer 26

* Adjusting amount of B, G and R light we can match the cone activations * Even though light patches are different

Question 27

What are metamers?

Answer 27

* Physically different stimuli that appear the same

Question 28

Describe monochromatism

Answer 28

* No functioning cones * Functioning rods * See world only in shades of gray * Very sensitive to light * Need to wear dark glasses during the day

Question 29

Describe the types of dichromats

Answer 29

* Protanopes * No L cone * ✖️ - Red and Green * ✔️ - Blue and Green, Blue and Red * 420 and 560nm * Deuteranopes * No M cone * ✖️ - Red and Green * ✔️ - Blue and Green, Blue and Red * 420 and 640nm * Tritanopes * No S cone * ✖️ - Blue and Green * ✔️ - Red and Green, Blue and Red * 560 and 640nm

Question 30

What are unilateral dichromats?

Answer 30

* Normal trichromatic vision in one eye but dichromatic vision in the other eye * Help with insight into dichromats * Protanopes and deuteranopes = See blue and yellowish-green * Tritanopes = See blue and red

Question 31

What is the opponent-process theory of colour vision?

Answer 31

* Colour we perceive is determined not only by cones * Signals from cones are processed by cortex where they are combined into 3 colour opponent channels * Red-green * Blue-yellow * White-black

Question 32

Describe afterimages ## Footnote Psychophysical evidence for Opponent-Process Theory of Colour Vision

Answer 32

* Viewing red stimulus - L cones more stimulated than M * Red percept activated more than green (suppressed) * Therefore see red * L cones habituate and become less sensitive to stimulus * White shown = Green stronger than red * Same for blue and yellow

Question 33

Describe impossible colours ## Footnote Psychophysical evidence for Opponent-Process Theory of Colour Vision

Answer 33

* Some colour combinations are impossible * ✔️- Bluish red (purple), yellowish red (orange), yellowish green * ✖️ - Can't perceive bluish yellow or reddish green * Blue + yellow light = White * Blue and yellow are opponent colours * Red + green light = Yellow * Red and green are opponent colours

Question 34

What is colour constancy?

Answer 34

* Colour of light an object reflects is determined not only be reflectance * Also by colour of light shining on it * White = Reflects colour of object * But enough of any other colour = Object reflects that colour because that is the only colour available * Light reflected determined by... * Reflectance x Illumination = Reflected light

Question 35

Why would we continue to see a green sweater as green even when it predominantly reflects green light?

Answer 35

* We habituate to the colour * Becoming less sensitive * We discount the illuminant